When a communication path is established between a calling and called party, if one of the parties to the call is associated with a key telephone system, it is possible for the key telephone party to place the call in the active but noncommunicating (hold) mode. In this mode the communication path between the parties is maintained active but communications cannot take place. The key telephone party can, by operation of the like key, return the call to the bidirectional communication state.
In some situations it is now possible to provide some form of entertainment, usually music, to the party who has been placed on hold.
It is desirable, for economic reasons, to use the same limit circuit to serve all stations whether or not the music-on-hold feature is provided. Such a system is described in U.S. Pat. No. 4,056,695 issued to Angner et al on Nov. 1, 1977. However, the system described in the above-mentioned circuit while constituting an improvement over prior art still exhibits problems with the music-on-hold arrangement. One problem is that connection of the music-on-hold feature requires rewiring of the line card to accommodate the connection of a connectorized daughter-board music receiver card to the line card. Another problem arises such that in certain applications spare terminals on the line card are not available to wire-in the music signal and hence a separately mounted music coupler card is required, this results in additional space allocation, additional wiring and duplication of hold control logic on the music receiver card. In addition, the existing music coupler cards use passive components which exhibit limited isolation between telephone lines sharing a common music source and could also exhibit signal loading problems when too many lines share a common music source.
Thus, a need exists in the art for a music receiver circuit adapted for easy connection to the line card of the type illustrated in U.S. Pat. No. 4,056,695. A further need exists for a music receiver card which will reduce the rewiring necessary to accommodate a music-on-hold feature, as well as reduce the signal loading caused by multiple music receivers, and improve the isolation between communication lines connected to a common music source.